Nifedipine reduces blood pressure predominantly by reducing systemic vascular resistance due to a direct vasodilating action on the arterioles. This peripheral vasodilation appears greater the more severe the hypertension. Studies have demonstrated an additive effect of beta blockers and converting-enzyme inhibitors in patients not controlled with nifedipine alone. Although there is a controversy about whether diuretics have an additive effect on blood pressure in patients already taking nifedipine, it would appear that the blood pressure-lowering effect of thiazide is blunted. Studies have shown that a high sodium intake may enhance the acute blood pressure-lowering effect of nifedipine. Nifedipine does cause a long-term reduction in sodium balance.